1. Field of the Invention
The present invention relates to an IP telephone and an IP telephone call method that enable a voice call over the Internet.
2. Description of Related Art
In recent years, various forms of IP telephone services that employ the VoIP (Voice over Internet Protocol) technology are provided. As an example of the IP telephone services, an SIP server on an IP network connects a call, according to the SIP (Session Initiation Protocol), between an IP telephone at a caller terminal and an IP telephone at a receiver terminal. After the call is connected, the IP telephones exchanges voice packets via the IP network, in order to realize the real-time telephone call.
In addition, as a technology for communicating image information via the IP network between different terminals, an Internet facsimile (IFAX) has been introduced. For such an IFAX service, the IETF (Internet Engineering Task Force) has made some recommendations on details of the data format (IFAX data format) to be exchanged over the IP network (RFC2305). For example, a document is scanned at an IFAX terminal, converted into a TIFF format, and further converted into e-mail data in the MIME format before transmitted to a mail server of the destination IFAX terminal. Then, the destination IFAX terminal (receiver terminal) receives the data from the mail server (POP server) (see Related Art 1, for example).                [Related Art 1] Specification of U.S. Pat. No. 6,614,891        
When an IP telephone with the IFAX function (telephone having both IFAX and IP telephone functions) has a voice call to another IP telephone with the IFAX function, the voice call must be terminated in order to transmit a document image to the call receiver. When the transmission of the image information (with the IFAX function) is finished, the caller must make another IP telephone call to the same party for continuing the voice call.